Basically, from what I'm led to believe, you deploy DryDrop to GAE, configure (domains, Github html repository etc.), then publish your static HTML by pushing to the GitHub repository (GitHub utilises 'hooks' to alert your DryDrop install to any new HTML changes).

I haven't used it personally, yet, but if the former CTO of Threadless Tees, Harper Reed, thinks it's OK, that's good enough for me :-D .